The invention relates generally to electrical position sensors for mechanical devices and more specifically to a sensor for the gear selecting mechanism of a transfer case which utilizes Hall effect sensors and a coded, apertured plate.
Nearly every motor vehicle manufactured requires an indication of the condition, i.e., current operating state, of the transmission for some purpose. In early vehicles with fully mechanical transmissions, such indication was achieved by the position of the gearshift lever and was visually provided to the driver. With the advent of automatic transmissions and the limited range of movement of the gearshift lever, a dedicated display providing a positive visual indication of a selected gear was provided. Such displays, in their earliest and least complicated form, included an arrow or gun sight attached to the shift lever which traversed a stationary, sequential display of indicia corresponding to the available gears. In their more complicated configurations, a movable series of such indicia were displayed in a fixed viewing window or a movable light selectively illuminated stationary, translucent indicia.
As transmission vehicle control systems became increasingly complicated, collected data regarding the selected transmission gear might be used not only to provide information to the driver but also for use by other vehicle systems. Such devices are illustrated and described in U.S. Pat Nos. 4,100,530, 4,882,572 and 4,896,135. Gear selection detection and indication systems may also be utilized in conjunction with vehicle diagnostics. A system of this type is presented in U.S. Pat. No. 5,021,764.
Such sensing, display and diagnostic systems utilize diverse sensors, controlled devices and readouts. In U.S. Pat. No. 5,111,180, a plurality of electrical contacts which are arranged to partially overlap, provide distinct combinations of signals which indicate distinct transmission positions. U.S. Pat. No. 5,420,565 teaches a system wherein plurality of electrical contacts, in conjunction with a pattern of conductive and non-conductive areas on a sector plate, provide a four-bit binary code which may be utilized to deduce the transmission position. The four-bit binary code is supplied to both a transmission controller and a visual display.
One drawback the foregoing devices have in common is a separation of the position sensor from the actual positioned elements of the transmission or gear box. That is, the sensor typically senses the position of a gearshift lever or component external to the transmission as opposed to the position of the internal mechanical elements themselves. In many instances this separation is of no consequence as there is little opportunity for a disparity to develop between the commanded position and the actual position of the mechanical components.
Other devices, particularly motor vehicle transfer cases, in which a shift may be commanded but the positioning of the internal components of the transfer case may, by design, be delayed until another vehicle condition such as an off throttle condition is achieved or may simply be impossible to achieve until some current operational condition of the vehicle and driveline has changed, however, present challenges. In order to more accurately detect and provide data regarding the actual physical position of the transfer case gear selection components, it is preferable that the detection mechanism sense the actual position thereof and thus be mounted within the transfer case itself. The present invention relates to such a device disposed within a transfer case.